In an electrically controlled throttle apparatus shown in FIG. 16, a driving device such as a motor controls an opening degree of a throttle valve 102 in accordance with a position of an accelerator pedal stepped by a driver. In the throttle apparatus, a clearance is formed between an inner periphery of a substantially tubular throttle body 101 and an outer circumferential periphery of a throttle valve 102, and the clearance has a large influence of an air tightness of the throttle apparatus when the throttle valve 102 is in its full close position.
Conventionally, the throttle body 101 and the throttle valve 102 are independently manufactured in each different process. Subsequently, a manufactured throttle valve 102 is combined with a manufactured throttle body 101 in accordance with an inner peripheral dimension of the manufactured throttle body 101 in a downstream process. Alternatively, a manufactured throttle body 101 is combined with a manufactured throttle valve 102 in accordance with an outer circumferential dimension of the throttle valve 102 in a downstream process. Thus, a predetermined clearance is obtained between the bore inner periphery of the throttle body 101 and the outer circumferential periphery of a throttle valve 102. A throttle shaft 103 integrally rotates with the throttle valve 102. Both of the ends of the throttle shaft 103 are rotatably supported by cylindrical bearings 104 provided in the throttle body 101.
U.S. Pat. No. 5,304,336, which is a counterpart of JP-5-141540A, shows molding methods in which a manufacturing process of the throttle body and the throttle valve is reduced. In the molding methods, the throttle body 101 and the throttle valve 102 shown in FIG. 17 are integrally molded of a resinous material in the same molding dies. At first, the substantially tubular throttle body 101 is integrally molded of a resinous material. Subsequently, inner periphery (bore inner periphery) of the throttle body 101 is used as a part of a molding die molding the throttle valve 102, and the throttle valve 102 is molded. Thus, a shape of an outer circumferential periphery of the throttle valve 102 is adapted to a shape of the bore inner periphery of the throttle body 101 in the above molding methods.
The molded throttle body 101 is gradually cooled in the body cavity to be solidified. Subsequently, the movable die is slid forward in order to form a valve cavity, into which a resinous material is filled. The throttle valve 102 is molded of a resinous material in the throttle body 101.
However, in the above molding methods of the throttle valve 102, the throttle body 101 is molded of a resinous material while the molded throttle body 101 is restricted by dies in its radial direction and in its substantially circumferential direction. Thus, the throttle valve 102 is molded of a resinous material while the throttle body 101 and the throttle valve 102 are restricted by the dies. The throttle body 101 and the throttle valve 102 are taken out of the dies, and gradually cooled. In this cooling period, the unrestricted throttle body 101 and the throttle valve 102 are contracted. The throttle body 101 and the throttle valve 102 are deformed. Accordingly, it is difficult to maintain the clearance in a predetermined dimension between the inner periphery of the throttle body 101 and the outer circumferential periphery of the throttle valve 102.
A practical use of the throttle apparatus releases an internal stress, by which the apparatus is deformed. When the throttle apparatus is made from a crystal resin and is crystallized, the apparatus is deformed due to the crystallization thereof. Even the apparatus is annealed or aged, the throttle body 101 and the throttle valve 102 are deformed individually.
To solve the above problem, the inventors filed Japanese patent application No. 2003-285434 on Aug. 1, 2003. In this application, the throttle valve and throttle body is formed in a same die in such a manner that the throttle valve 102 is opened in a predetermined angle as shown in FIG. 18. As shown in FIG. 19, the molding dies include a first insert die 121 and a second insert die 122. The first insert die 121 is disposed in the fixed die and has a first valve cavity 111 to form a first semi-circle plate 106. The second insert die 122 is disposed in the movable die and has a second valve cavity 112 to form a second semi-circle plate 107. FIG. 20 shows a valve gate by an arrow 123, through which a melted resin material is injected into the first and the second valve cavity 111, 112. An air in the cavity and a gas generated from the injected resin remain in a lower portion of the cavity to cause a defect of the throttle valve 102. That is, the melted resin material flows into the cavity 111, 112 from the top of the cavity 112 and flows down to the bottom of the cavity 111. The air and the gas cannot be purged from the cavity, so that a shortshot where the melted resin material is not charged can be generated as shown in FIG. 21. Alternatively, a corrosion can be generated by the gas at the bottom end of the throttle valve 106.
When the valve gate is disposed at a side surface of a throttle shaft 103, the melted resin material flows from the center of the throttle valve 102 to the outer periphery of the throttle valve 102. The air and the gas are pushed toward the radial end of the throttle valve 102, by which the shortshot and/or the corrosion by the gas can be generated as shown in FIG. 23.
The circularity of the throttle valve 102 is deteriorated. Thus, when the throttle valve 102 closes the throttle body 101, a clearance between the inner surface of the throttle body 101 and the outer surface of the throttle valve 102 becomes large to increase an air leakage there between.